JFrame doesn't load for multiple clients

Question

I am not able to load JFrame for multiple clients whereas it works fine for a single client. I am able to perform all the operations on a single client. The frame becomes visible but the contents are not.

Do I need to add something extra? Am I making the correct connections?I am running it on my local machine.

Can I run multiple instances on the same machine?

Server :

public class ServerThread extends Thread{
    public static void main(String[] args) throws IOException {
        EventQueue.invokeLater(new Runnable() {
        public void run() {
            try {
                ServerSocket serverSocket = new ServerSocket(4518);
                while(true){
                Socket clientSocket = serverSocket.accept();
                Thread window=new Frame1();
                window.start();
                }
            } catch (Exception e) {
                e.printStackTrace();
            }

Client:

    public class Client extends JFrame{
    public static void main(String arg[]){
        String hostName="localhost";
        int portNumber=4518;
       try{
            Socket echoSocket = new Socket(hostName, portNumber);
            PrintWriter out =
                new PrintWriter(echoSocket.getOutputStream(), true);
            BufferedReader in =
                new BufferedReader(
                    new InputStreamReader(echoSocket.getInputStream()));

        }

JFrame:

public class Frame1 extends Thread{

    static JFrame frame;
    private static JTextField textField;
    private static JPasswordField passwordField;
    static Connection conn = null;
    static PreparedStatement pst = null;
    static ResultSet rs = null;
public Frame1() {
        System.out.println("hello");
        initialize();
    }
private static void initialize() {
        frame = new JFrame();
        frame.setVisible(true);
        frame.setTitle("Course Registration- Spring 2017");
        frame.getContentPane().setBackground(new Color(204, 204, 255));
        frame.setBounds(100, 100, 450, 300);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().setLayout(null);

        JButton btnNewButton = new JButton("Sign in");
        btnNewButton.setBackground(new Color(204, 102, 153));
        btnNewButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                conn = DBConnect.DBConnect();
                String sql = "Select * from users where username =? and password=?";
                try{
                    String userName=textField.getText();
                    String password=passwordField.getText();
                    pst = conn.prepareStatement(sql);
                    pst.setString(1, userName);
                    pst.setString(2, password);
                    rs = pst.executeQuery();

                    if(userName.equals("admin") && password.equals("admin")){
                        ServerSideViews s = new ServerSideViews();
                        s.setVisible(true);
                        s.setUserName(userName);
                        s.setFrameLogin(frame);
                        System.out.println(userName);
                        frame.setVisible(false);
                    }

                    else if(rs.next() && !(userName.equals("admin"))){
                        JOptionPane.showMessageDialog(null, "Welcome " + textField.getText() );
                        CourseRegistration c = new CourseRegistration();
                        c.setVisible(true);
                        c.setFrameLogin(frame);
                        frame.setVisible(false);
                        String sql1 = "Select major from users where username=?;";
                        System.out.println(sql1);
                        pst = conn.prepareStatement(sql1);
                        pst.setString(1, userName);
                        rs = pst.executeQuery();
                        String major="";
                        while(rs.next())
                        {
                        major=rs.getString("major");
                        }
                        c.setUserName(userName);
                        c.comboBox.setSelectedItem(major);
                        c.comboBox.disable();
                    }
                    else{
                        JOptionPane.showMessageDialog(null, "Invalid user name or password");           
                    }
                }catch(Exception e1){
                        e1.printStackTrace();
                }   
            }
        });


        btnNewButton.setBounds(157, 182, 117, 29);
        frame.getContentPane().add(btnNewButton);

        JLabel lblUserName = new JLabel("User Name");
        lblUserName.setBounds(76, 96, 86, 16);
        frame.getContentPane().add(lblUserName);

        JLabel lblPassword = new JLabel("Password");
        lblPassword.setBounds(86, 129, 61, 16);
        frame.getContentPane().add(lblPassword);

        textField = new JTextField();
        textField.setBounds(157, 91, 130, 26);
        frame.getContentPane().add(textField);
        textField.setColumns(10);

        JButton btnNewButton_1 = new JButton("Register");
        btnNewButton_1.setBackground(new Color(51, 102, 204));
        btnNewButton_1.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                UserRegistration reg = new UserRegistration();  
                reg.setVisible(true);
                reg.setFrameLogin(frame);
                frame.setVisible(false);
            }
        });
        btnNewButton_1.setBounds(157, 225, 117, 29);
        frame.getContentPane().add(btnNewButton_1);

        passwordField = new JPasswordField();
        passwordField.setBounds(157, 124, 130, 26);
        frame.getContentPane().add(passwordField);

        JLabel lblNewLabel = new JLabel("Course Registration - Spring 2017");
        lblNewLabel.setBounds(109, 24, 241, 16);
        frame.getContentPane().add(lblNewLabel);
    }
}

Answer 1

Don't start a task that blocks on the Event Dispatch Thread (EDT). The GUI won't be able to respond to events.

So don't start the ServerSocket from the SwingUtilities.invokeLater(..).

Instead you need to use a separate Thread for the ServerSocket.

Read the section from the Swing tutorial on Concurrency for more information and examples.